Twin tube style dampers or shock absorbers are commonly used as part of a suspension system for automobiles, trucks, motorcycles, all-terrain vehicles (ATV), bicycles, industrial equipment and the like for absorbing and dissipating energy. A conventional twin tube type damper generally includes an inner fluid chamber that is at least partially defined by an inner tube, an outer fluid chamber defined by an outer tube that is in fluid communication with the inner fluid chamber, a piston assembly that extends into the inner tube and a spring such as an air spring or a helical spring. Certain twin tube style dampers also include a fluid reservoir that is in fluid communication with the inner and the outer fluid chambers via various fluid circuits. A damping fluid fills the inner and the outer fluid chambers and a portion of the fluid reservoir.
The piston assembly includes a disk shaped piston that is disposed within the inner tube and that is attached to a piston shaft. The piston may include one or more orifices that provide for fluid communication through the piston. The damper is coupled at opposing ends to movable portions of the suspension system. As the movable portions of the suspension move relative to each other, the piston shaft and the piston translate within the inner tube between a compression stroke and a rebound stroke.
During the compression stroke, the damper works in conjunction with the spring to control the displacement and velocity of the piston shaft by metering the damping fluid from one side of the piston to the other, either by moving fluid directly through orifices in the piston or through fluid flow channels between the inner fluid chamber and the outer fluid chamber. In the case where a fluid reservoir is used, fluid is additionally displaced to the reservoir via the various fluid circuits. During the rebound stroke, the damper works against the spring to control the displacement and velocity of the piston shaft by metering the damping fluid from one side of the piston to the other, either by moving fluid directly through orifices in the piston or through fluid flow channels between the inner fluid chamber and the outer fluid chamber. In the case where a fluid reservoir is used, fluid is additionally recovered from the reservoir via the various fluid circuits.
Damping may be controlled by providing various valves and orifices within the fluid circuits through which the damping fluid flows. Damping responsiveness of a conventional damper is generally limited by the orifice size and/or by the number of the fluid circuits. For example, relatively smaller orifices restrict fluid flow through the fluid circuits, thus stiffening the damper, and relatively larger orifices allow for increased fluid flow resulting in less resistance through the fluid circuits, thus softening the damper. In certain conventional dampers, damping responsiveness may be tuned by adjusting the various damping valves.
Damping characteristics (damper tunes) of twin tube dampers are generally determined by adjustable damping valves. Adjustment of these damping valves generally requires either internal modification of the damper and/or adjustment of incremental external adjusters. In the case of internal modification, this means the damper must be at least partially disassembled, changed internally, and then reassembled for the damping to be modified. However, this is impractical to do while the damper is in use. In the case of incremental external adjustments, the adjusters can be changed without disassembling the damper. In either case, the damping characteristics during use of the damper are limited to the single characteristic damping tune determined by the chosen adjustment of the damper.
This single damper tune may not be the desired damper tune for a certain range of conditions/situations experienced during use of the damper. For example, in high performance applications such as when used on a motorcycle, ATV, snowmobile, bicycle, automobile, truck and/or when used for racing applications, the terrain, speed, and environmental conditions may require various or changing damping characteristics. Therefore, an improved twin tube damper that allows at least two predefined damping tunes, each quickly and possibly remotely accessible during use of the damper would be useful. In addition, it would be further useful if each damper tune was itself fully definable either externally or internally, such that compression stroke damping and the rebound stroke damping were each altered as desired between the various defined damping characteristics.